Tire Size & Steering Question

[Xusia]

This is probably a question more for those that have built roadsters, but certainly anyone with insight is welcome to comment. I appreciate ALL perspectives!

The question is around front tire size. I'm leaning toward running 245/40-17 all around (NOT set in stone), and am wondering how much more difficult that will be to steer than a 225/45-17 (my other - and oft discussed in this forum - front tire size choice).

Background, not directly relevant to the question, but for those that care
My reason is wheel size. I want to stick with close-to-stock rolling circumference to maintain speedo accuracy. I also want to maintian a minimum sidewall height to prevent wheel damage. These 2 combined dictate 17" wheels (I can't get the sidewall height I want while maintaining the stock rolling circumference using an 18" wheel). The problem I've found shopping is that I haven't found even a moderately priced wheel (didn't look at the expensive ones) that is offered in 2 different, appropriate widths in a 17" diameter (i.e. 17x7 or 7.5 for the front, and 17x8.5 or 9 for the rear). I'm really hoping the wheels FFR offers solves this, but I'm almost certain the rears they offer will be 18".

So the simplest solution is to run the same wheel all around (i.e. 17x8.5 or 9). However, this makes a 225 a really poor choice.

So... Opinions? Ideas?

THANKS a bunch in advance folks.

[Evan78]

My thought would be 245/225 = 1.09, so approximately 9% more effort.

I'm not sure what options are available for adjusting the Subaru speedometer, if any, but you could use a GPS speedometer/odometer instead.

[Xusia]

For cost and ease of build considerations, I'd like to use the stock dash as is. I'm sure I could get it recalibrated, and if all else fails, that might be the route I need to go, but a couple other thoughts are making that a less preferred route:

• 18" wheels with additional sidewall height will add significant weight compared to a 17"
• 18" wheels with additional sidewall height are starting to get pretty big, raising clearance concerns as well as how it would look compared to the wheel well opening.

[skullandbones]

I am still in limbo with this question on my roadster as I have not actually tried the tires I want on it yet. However, I have communicated with the manager at my local Discount Tire about the project. I buy all my tires there and they have been most helpful for the routine tire needs I've had in the past. However, he assures me that they will take as good care of my special project as the other cars. So he has offered to trial fit until we get it right. I've test fit the wheels I plan on using. They are 17x9 Cobra Rs all round. So after discussing it with DT, they have recommended dia/size of front: 25 in - 255/40-17 or 24.7 in - 245/40-17 and rear: 26 in - 285/40-17 or 25.7 in - 275/40-17. I have a wider rear diff (95 Cobra Mustang) so I have to be careful of clearance. I think it will be a good start for mine but like I said it is not done yet and will depend on fitment at the shop. I will let you know if you like. I am not as concerned about maximizing the rears since I am only running 350 to 375 bhp. Hope that helps. WEK.

[Evan78]

If you want more wheel selection, maybe you should also consider using 5x114 hubs.

[Xusia]

My donor has 5x100 hubs, making 5x114 hubs an additional purchase. And - more importantly - FFR does not currently support the use of 5x114 hubs. This means I'd be doing custom work - not really what I want to be doing as a first time builder with low to moderate (at best!) mechanical skills.

I've seen a lot of suggestiong - and thanks for those guys! - but no one has really responded to the question of how much more difficult, if at all, the 818 will be to steer with 245s on the front rather than 225s. skullandbones post above, where he is going to use 245s or 255s on the front of his heavier Roadster, leads me to conclude it will prob be fine. I'm just hoping to hear from someone with actual experience with a tire that wide (or wider) on a car with manual steering.

[Evan78]

I don't see any simple answers, other than "it will be fine". It sounds like you either want wheels that meet your specs or reassurance about your plan. Anything else is likely to require additional work, time, and money.

Are you sure you're going to run without power steering? If you keep that, steering effort seems like a non-issue.

[skullandbones]

Sorry Xusia. I forgot to mention I am running PS. I like it so far and I can run increased castor and still not have a steering effort issue. But I have seen somewhere that a roadster should not run more than about 8.5 inches of rubber in front. I think the 818 will handle that with the lighter weight and more radical weight distribution, IMO. WEK.

[Silvertop]

This is probably a question more for those that have built roadsters, but certainly anyone with insight is welcome to comment. I appreciate ALL perspectives!

The question is around front tire size. I'm leaning toward running 245/40-17 all around (NOT set in stone), and am wondering how much more difficult that will be to steer than a 225/45-17 (my other - and oft discussed in this forum - front tire size choice).

Background, not directly relevant to the question, but for those that care
My reason is wheel size. I want to stick with close-to-stock rolling circumference to maintain speedo accuracy. I also want to maintian a minimum sidewall height to prevent wheel damage. These 2 combined dictate 17" wheels (I can't get the sidewall height I want while maintaining the stock rolling circumference using an 18" wheel). The problem I've found shopping is that I haven't found even a moderately priced wheel (didn't look at the expensive ones) that is offered in 2 different, appropriate widths in a 17" diameter (i.e. 17x7 or 7.5 for the front, and 17x8.5 or 9 for the rear). I'm really hoping the wheels FFR offers solves this, but I'm almost certain the rears they offer will be 18".

So the simplest solution is to run the same wheel all around (i.e. 17x8.5 or 9). However, this makes a 225 a really poor choice.

So... Opinions? Ideas?

THANKS a bunch in advance folks.

Why not go with 17 X 8.5's? This size is within acceptable mounting range for a 225/45-17 for the front and a 255/40-17 for the rear, and both tire sizes yield a 25" diameter tire (at least on the tire that I checked it against, a Bridgestone 011A), which is what you need to keep your speedometer right.

[Xusia]

That was my front running plan, but the guy at the tire store said "Technically it will fit, but its not the best choice because the has to stretch to fit." I'd also prefer a bit of overhang to protect the wheel from curb damage. Ig it's stretching to fit, I'm thinking I won't have any overhang.

If it matters, I'm leaning toward the Federal 595 RS-R.

[Silvertop]

Another choice is to simply use stock WRX 16 X 6.5" wheels, with 205/55-16's on the front and 225/50-16's on the rear. Many on the forum are likely to pooh-pooh this combination as not enough tire, but if you are really building a pure streeter and are not planning on producing great sacks of horsepower, these tires will provide enough adhesion to take you around virtually any corner while severely fracturing any speed limit in the land. With the money you save, you can probably buy an LSD which will help you get decent launches even with the narrower tires.

Probably not what you want -- but it'll work. It's what I'm going to do.

[Xusia]

LOL - If my donor would have had decent wheels, that's EXACTLY what I would do. But since I have to spend some money, I figured I might as well get a better wheel. I'm definitely in the budget wheel category, and they will probably weight close to the stock ones because of it. I could probably save some money by finding a stock set of wheels, but my engine is putting out a fair amount of ponies, so I reason the better wheels (and more tire width) are a reasonable upgrade expenditure.

[Silvertop]

LOL - If my donor would have had decent wheels, that's EXACTLY what I would do. But since I have to spend some money, I figured I might as well get a better wheel. I'm definitely in the budget wheel category, and they will probably weight close to the stock ones because of it. I could probably save some money by finding a stock set of wheels, but my engine is putting out a fair amount of ponies, so I reason the better wheels (and more tire width) are a reasonable upgrade expenditure.

Then your only real choice is to keep shopping for some good-looking affordable 17" wheels available in the appropriate different widths. There's got to be something out there somewhere. For what it's worth, if I wasn't committed to using the stock wheels that came with my donor, I'd be shopping for 17" wheels just like you. Good Hunting!

[Evan78]

Rota makes several wheels available in the sizes you're looking for. Here's some 17" wheels.

I went to the bottom of the list (17x9) and then did a search on the names to see if there were also narrower versions. I stopped after the first 4 models (Torque, Titan, Grid, DPT). There might be more.

[Xusia]

Thanks! I'll look that up. I like the Rotas I've seen.

[Grintch]

I have an STI with 245/40-17s. There is no issue with them being too much tire, and 255, 265, and even 275 have reportedly been used with no steering issues. If you use a manual/depowered rack you might have some issues at the higher end of that size range, especially at parking lot speeds, but a lighter car is always easier to steer than a heavy one so its hard to say where a reasonable limit would be with the 818. This will also be somewhat dependant on the caster & geometry of the FFR suspension. For wider tires, 255 and above, 18 inch wheels tends to give you more options and I suspect that given the drastic change in weight distribution, it will likely be advantgeous to run wider rear tires. Rota does seem to offer the most 5x100 options, especially in wheels wider than 8 1/2".

[IMPREZvWRX]

wheeldude.com is a good place to find 5x100 wheels in various diameters/widths/colors. He also does a lot of custom wheel group buys for the crazy stuff.

[Ironhydroxide]

if you really wanted to get into it, you could have a custom speedo gear cut out of bronze. then you could run any tire size you want, and have the speedo accurate.

[bnr32jason]

Or just get a GPS speedo.

[GJerry]

I am running 245/45-17 on Halibrand Cobra lll wheels all around. With an un-powered steering rack, driving effort was ok but parking effort was tuff. I switched to a 20:1 (4 turns lock to lock) manual rack and parking effort was greatly improved with out much noticable ill effect on street driving response.
Hope this helps.

[tirod]

Finding tire sizes has become an obstacle these days. Rather than fight it, find out what the supplier of your favorite brand offers and work with the size you can get.

The difference in the extra 20mm of tire isn't likely to be huge, and probably arguable if it's even significant. The depowered rack is likely going to be a bigger issue, because they are quick lock to lock with less mechanical advantage. That means turning will take more foot pounds of force by your upper torso.

Ran a '66 Mustang in the day, manual steering, and added Shelby quick steer idler and pitman arms. Really cut down the turns lock to lock, and with the G70-14's I stuffed under the fenders, it was a lot harder to turn parked by the curb. Rolling away, tho, ok. Turning a tire thru it's scrub radius at a dead stop with manual steering is always going to be harder than power steering, turning one with power steering nearly regardless of size is still easy.

I wouldn't sweat the tire size for steering effort, worry about finding tires as wide as you want - at least 17's are available. You want to hear some bellyaching and whining, ask guys trying to find wide rubber for 15" rims. Other than a few retro rubber makers, they don't exist. The market moved up and left them behind.

[GJerry]

Sorry forgot to mention that's on my Cobra not an 818!

[Grintch]

I wouldn't sweat the tire size for steering effort, worry about finding tires as wide as you want - at least 17's are available. You want to hear some bellyaching and whining, ask guys trying to find wide rubber for 15" rims. Other than a few retro rubber makers, they don't exist. The market moved up and left them behind.

Oddly enough, race tires seem to lag behind street tires in the diameter race. R compounds get thin at 19" and almost none at 20". Real slicks still have very strong availability in 13" and 15". I guess it just goes to show the "dub" look really is all about looks.

[tirod]

The smaller overall diameter allows better gearing on the track. Many racers are using light steel wheels and they have to be safety certified anyway. Bigger rims results in more unsprung weight, which is detrimental to handling, and brake technology has improved enough that huge rotors aren't necessary to get good performance.

There's a Car and Driver article on their website testing the same type tires on increasing rim sizes. The tradeoff on the track going to a bigger rim is the shorter sidewall - it's not an apples and oranges comparision when aspect ratio changes as the rim size goes up. A shorter sidewall is stiffer and reacts with less flex, making the car turn in more sharply with reduced lag. On the other hand, diameter keeps increasing and gear ratio is lost, which slows acceleration, plus the tire/wheel assembly gets heavier, resulting in more work for the springs and shocks. Those are significant disadvantages.

On the street, low profile tires on big rims can't handle a serious pot hole, tho, and there are a lot of folks with busted rims who found out the hard way. All that goes to increases sales of tires and rims for an incremental difference in street driving that really amounts to nothing. Entirely normal in the hot rod industry, they market "speed" and we buy it because it's "race car," which means we're bigger studs than you. It's not reality or actual performance, it's about social standing.

Therefore, because Joe Suburban drives the market with his lack of education and huge monetary incentives, we get stuck with the tires and rims that aren't really optimum on the street, and the racers get the tires they need for the track. There is a line in the sand, and until someone can make big heavy tires and rims work on the track, racers are sticking to what they know works.

[Xusia]

That reminds me a lot of the motorcycle industry a while back. There was a move to wider rear wheels, with an associated move to wider rear tires. Unfortunately at the time those wider rear tires were only available in a lower profile (50 series; i.e. 190/50). This did NOT improve handling or grip. Most racers were running 180/55 tires on the wider wheels because they had less rotational mass and because the taller profile actually provided more contact patch at lean and quicker steering. As soon as the stock 190/50 was used up, I switched to a 180/55 and never looked back. This move was seemingly all done because public perception was that "wider is better."

Now the wider tires are available in the taller 55 series profile, so it's all good (although it is still more rotational mass), but it's a similar example to the above!

Bit of a tangent, I know, but since I'm the OP I figure I'm allowed! LOL

[Silvertop]

That reminds me a lot of the motorcycle industry a while back. There was a move to wider rear wheels, with an associated move to wider rear tires. Unfortunately at the time those wider rear tires were only available in a lower profile (50 series; i.e. 190/50). This did NOT improve handling or grip. Most racers were running 180/55 tires on the wider wheels because they had less rotational mass and because the taller profile actually provided more contact patch at lean and quicker steering. As soon as the stock 190/50 was used up, I switched to a 180/55 and never looked back. This move was seemingly all done because public perception was that "wider is better."

Now the wider tires are available in the taller 55 series profile, so it's all good (although it is still more rotational mass), but it's a similar example to the above!

Bit of a tangent, I know, but since I'm the OP I figure I'm allowed! LOL

Perfectly valid perspective, and relevant to the original thread concept, IMO. Something to think about when selecting tire and wheel sizes.