Wheel size for handling

[RebekahsZ]

Thanks for the examples, johnc. The answers come with testing. That is why we do qualifying races for bracket racing-to see where the car is running TODAY. As the temperature and humidity drop into the night, everything changes. And testing is expensive. CobraMatt recently talked with me and described how he wound up totalling out his Corvette in testing (not at a race) just to get the angle optimized on his rear wing. Had to reconstruct car to get back to testing.

 

Jesse-my argument for 17" wheels is brake clearance and availability of used race tires (Hoosiers). I'm working my way into 275/40?/17s for that very reason-lots of those available from the S2000s and Mustangs. The most readily available 15" race tire is the 205/50/15 from the Spec Miata bunch. There are always lots of R6s available in that size for CHEAP. Everytime you change diameters you gotta spend $1000-ish on wheels. I'd go straight to 17s so you don't have a bunch of wheels and tires you can't get rid of when you upgrade your brakes next year.

[JMortensen]

You can get the 12" wilwood setups under a lot of 15" wheels. FWIW.

[RebekahsZ]

I too, have read that some 15" wheels will fit. Unfortunately, mine do not. A set of AZC brakes are in the mail to me right now to be installed in November/December. I will be willing to let folks send me any wheel for test fitting. Dave test fit a wheel that I sent him and it took him like six weeks to get to it and two months before I got my wheel back, with me calling him every week to remind him-super nice guy, though. My 15" wheels will require a 1" spacer to fit, which will push the tire out of the wheel well. So, I'm going to have to order $400 worth of new rear wheels with a 1" larger back spacing to keep the tire in the wheel well. I plan to do a write-up. Unfortunately, I haven't found anyone who has catalogued WHICH 15" wheels will fit. I will try to do that based on any wheels folks chose to send me.

[Jesse OBrien]

I too, have read that some 15" wheels will fit. Unfortunately, mine do not. A set of AZC brakes are in the mail to me right now to be installed in November/December. I will be willing to let folks send me any wheel for test fitting. Dave test fit a wheel that I sent him and it took him like six weeks to get to it and two months before I got my wheel back, with me calling him every week to remind him-super nice guy, though. My 15" wheels will require a 1" spacer to fit, which will push the tire out of the wheel well. So, I'm going to have to order $400 worth of new rear wheels with a 1" larger back spacing to keep the tire in the wheel well. I plan to do a write-up. Unfortunately, I haven't found anyone who has catalogued WHICH 15" wheels will fit. I will try to do that based on any wheels folks chose to send me.

That sounds like a great project, 15" wheels are more budget-friendly on both wheels AND tires than 17" (I've had a very hard time finding inexpensive steel race wheels in 17", but there are piles of manufacturers making quality 15" wheels). Your point about Spec Miata (and spec e30, if I remember correctly) tires lends even more value to the inexpensive wheels. While I don't hate the idea of overfenders or spacers, it'd be nice to know what would fit on which brakes without any modifications. It'd also be nice to know which wheels interfere with suspension components.

 

The PROBLEM I see with 15" wheels is that they're really only common for 205 and 225 widths. Anything wider and 17" is really necessary. Because I'm running a stock l28 on SU's, mostly-stock suspension, and this will be my first season racing, available grip isn't going to be the limiting factor and I don't expect to bump up against the limits of those tires.

[JMortensen]

Don't forget the Hoosier 15x10 option. Hoosier's 275/35/15 is a very popular size for autox and would be a good choice for a hillclimb car.

[heavy85]

Don't forget the Hoosier 15x10 option. Hoosier's 275/35/15 is a very popular size for autox and would be a good choice for a hillclimb car.

True and what I currently run for Hillclimb only. Problem with 15 is other than these Hoosier 275 Race tires or 9.5" slicks there is nothing bigger than 225. Especially true for street tires. 17" opens up lots of 245/255 options in all kinds of tires. The reason at the time for my 17's was rotor clearance for street driving. I have since been using thise rims with street tires but for racing in classes that requires 140/200 treadwear tires. 15 Diamonds steel race rims barely clear the caliper but the al street rims dont. Also need to consider 15's are typically 23" diameter where the 17's are about 25" so gearing, ground clearance (I bottom a lot on hillclimb with the 15's), etc also come into play.

[tube80z]

 

There's already been a lot of discussion on this but I thought I'd chime in with my take.  For hillclimb how fast you can get the tire up to operating temp is critical to help minimize run time.  Generally you'd want the smaller wheel for less rotating mass, which helps both acceleration and braking.  But many times the larger tires may be better developed by a manufacturer and that trumps the lighter weight.  You also really want a plan in place so you don't end up buying things more than once, which has a tendency to get really expensive.  For both autox and hillclimb you don't need huge brakes so you can run smaller wheels.  But that limits your tire choice and many of the better tires that heat up quickly are in larger wheel sizes.

 

JohnC mentioned the advantage of AWD for hillclimbs.  What I've found is that it's better at launch and then only if you have traction limited areas on the course.  2WD is often faster if the launch can be close because you have less weight running up the hill.  In the PNW our hills are often very steep with sharp corners and you'd think AWD would be king but there are many fast record holding cars that are only 2WD.  George Bowland came out a few years ago and decimated the records at most of the hills with his snowmobile powered AM car.  But those records are getting close to being taken down buy a 2WD Locost running LS power.  

 

For what it's worth my Z (Braaps old car) is setup to run 13 inch diameter wheels and 10.5 inch brakes.  I prefer less rotating mass and the smaller mass of the tires help them to heat up faster.  Good luck and be safe.  Hillclimbs are some of the most fun you can have but they have a high level of risk you need to manage.

 

Hope this helps,

Cary

[Jesse OBrien]

I'm trying to do more listening than talking in this thread, but I had to jump in here.

 

There's already been a lot of discussion on this but I thought I'd chime in with my take.  For hillclimb how fast you can get the tire up to operating temp is critical to help minimize run time.  Generally you'd want the smaller wheel for less rotating mass, which helps both acceleration and braking.  But many times the larger tires may be better developed by a manufacturer and that trumps the lighter weight.  You also really want a plan in place so you don't end up buying things more than once, which has a tendency to get really expensive.  For both autox and hillclimb you don't need huge brakes so you can run smaller wheels.  But that limits your tire choice and many of the better tires that heat up quickly are in larger wheel sizes.

 

JohnC mentioned the advantage of AWD for hillclimbs.  What I've found is that it's better at launch and then only if you have traction limited areas on the course.  2WD is often faster if the launch can be close because you have less weight running up the hill.  In the PNW our hills are often very steep with sharp corners and you'd think AWD would be king but there are many fast record holding cars that are only 2WD.  George Bowland came out a few years ago and decimated the records at most of the hills with his snowmobile powered AM car.  But those records are getting close to being taken down buy a 2WD Locost running LS power.  

 

For what it's worth my Z (Braaps old car) is setup to run 13 inch diameter wheels and 10.5 inch brakes.  I prefer less rotating mass and the smaller mass of the tires help them to heat up faster.  Good luck and be safe.  Hillclimbs are some of the most fun you can have but they have a high level of risk you need to manage.

 

Hope this helps,

Cary

Based on the one hillclimb event I've attended in person, I've noticed that corners are heavily cambered here. The hills are reasonably steep but the corners allow a lot of momentum to be carried through them. Even stock Miatas with sticky tires and aggressive drivers can put down impressive times. All the experienced drivers I've talked to recommend starting on street tires for slow, forgiving handling. Despite the added cost associated with changing wheels in another season or two, I think I'm going with some inexpensive 15x8 steel wheels for now with some 'grippy' DOT street tires on them. I still have a lot of research to do for prep, from a good roll bar to basic suspension tuning, then I think I'm going to get a small HF trailer and fab up a tow mount for it so I can haul some tools, spare parts, and wheels out to the events.

 

I'm looking forward to next season quite a lot, thanks for all the advice so far everyone. It's extremely helpful.

[tube80z]

If you have never hillclimbed before you should probably start with autox events where you can learn your car at high force levels and low speed.  Then drive about 80 to 90 percent of that for the hillclimbs and that leaves some margin for when things don't quite go to plan.  The majority of the people I see crash try and autox a hill and that's generally asking for trouble.

 

For race tires you can always get some used tires in a harder compound that don't grip as well for getting into this.  Then step up to the grippy stuff once you're reasonably comfortable.  

 

Hope that helps,

Cary

[Jesse OBrien]

I've been talking to some of the more experienced local hillclimbers (many have been doing this for as long as I've been legal to drive) about more standard scca/hpde/autox events and they all suggest starting by killing some pylons instead of trees to start out. They also universally recommend high treadwear tires for the first season, which is advice I took. I picked up some 195-60-14 wheels to pop on my 14x7 wheels for a combination of early season abuse and everyday driving. Once I've grown into them (which could take a couple seasons, if I'm honest with myself), I'd like to have my next step laid out clearly before me. Hopefully those 14" wheels will be mounted up by this weekend and I'll be able to roll the car around and reorganize my garage, at least!

 

I hate to admit it, but I think I'm more excited about the thought of a tire trailer behind an s30 than I am about the tires themselves.

[Phantom]

As intimated above the wheels need to be matched to the size tires you are planning to run.  The wheel width affects the sidewall fexure of the tire.  An an improper match can result in a sidewall flex that changes the contact angle of the tread with a resultant loss in total traction.  Kind of like when the rear end squats during heavy acceleration.  There are so many factors involved that it drives most folks nuts when they try to determine the best combination.

[Gollum]

Necropost because racecar. So cute to see how Jesse's grown.... Literally (as far as contact patch goes at least)

 

[Jesse OBrien]

Yeah, it's taken awhile to get some first-hand experience together, but after a few seasons of hillclimbing and autox here's what I've learned:
 

Quote

Ultimate grip doesn't matter unless the car is balanced.

 

I ran my Miatas with an array of tires, starting with Kumho XS in 205 width on stock tires. Then I went up to 15x8 on 225-50R15 DOT tires. Those went on my na8 Miata, and I decided to bump up to the new 245-40R15 DOT VR-1 tires from Maxxis (mostly for the gearing improvement). After some mounting issues on my 15x8 wheels (they really belong on wider wheels), I settled on 225/45R15 v720's for the 1.8liter Miata.

 

When these 15x13 m28 throwaways came with the box truck I bought, I was absolutely blown away by how lightweight they are. Spun wheels are similarly inexpensive, and I can get qualifying take-offs cheap through a hillclimbing friend. That seems like a good reason to give them a test, I'm a big fan of reducing unsprung weight while increasing mechanical grip. The 10" wide would probably be a better idea for what I'm doing, but we'll cross that bridge when I actually purchase tires.

[franky240z]

For all out handling you'll be wanting a reduction in unsprung weight.    However it all depends on your suspension also.

 

It should be possible to stone people who fit 17" wheels to the early s30 range.

 

 

[Gollum]

On 2/17/2018 at 1:52 AM, franky240z said:

For all out handling you'll be wanting a reduction in unsprung weight.    However it all depends on your suspension also.

 

It should be possible to stone people who fit 17" wheels to the early s30 range.

 

 

 Then can we stone the tire manufactures? They're the whole reason Chris organized the very successful rota group buy. Wide 16" tires were disappearing, and it's only gotten worse. I wish a short tire that fit a 15x8+ wheel was common, but they're not. You're super limited for DOT rubber and it's not cheap.

[JMortensen]

Heh. Looks familiar...

[turbogrill]

What is wrong with 15x10?

 

For something grippy, street legal and durable you can fit  RS4 or VR-1 245s. 

 

Larger wheels are just heaiver and more expensive.

[Gollum]

18 hours ago, turbogrill said:

What is wrong with 15x10?

 

For something grippy, street legal and durable you can fit  RS4 or VR-1 245s. 

 

Larger wheels are just heaiver and more expensive.

You just proved my point. If you want more than 245 tread your "15 wheel tire options are literally counted on a hand. Stepping up to 16" wheels means you get a few hands to count. 17" wheels actually start to get you multiple options from every manufacturer. It sadly means you're running wheel heights around 27" though, which is huge on a s30 imo.

[turbogrill]

5 hours ago, Gollum said:

You just proved my point. If you want more than 245 tread your "15 wheel tire options are literally counted on a hand. Stepping up to 16" wheels means you get a few hands to count. 17" wheels actually start to get you multiple options from every manufacturer. It sadly means you're running wheel heights around 27" though, which is huge on a s30 imo.

Oh...more than 245..yes you are probably right. 

245 is plenty for me