I already planing my next tires even though I have less than 2k on the ones I just bought, just because I am that addicted.

Right now I have 205/45R16 F1 GS-D3 and I am interested in getting 205/40R16 Falken RT-615 (same load rating and my wheels are 7" wide) but the OD is alot smaller than stock. I know RT-615 also come in 215/45R16 but i heard that 215 is wider than neccesary esp. for a non-S. In terms of of spedo/odometer accuracy and mpg/reduced final drive, I dont really care as I am not going to sell the car, I like acceleration better than top speed, and if I think i am going faster than it will be harder get a speeding ticket. But... when looking about I found this note on 1010tires:

When changing tire sizes, we recommend staying within 3% of the diameter of the original tire. Any more than this and you face the risk of brake failure.

I know my 205/45 are 4.83% smaller but 205/40 are 8.15% smaller. I was fine with the 205/45 cuz i have seen and talked to 205/45R16 owners and it was less than the 5% i saw somewhere else. Will a difference of 8% actually mess up my brakes/ABS settings etc, or is that to stop people putting 22" rims that weight 80lbs without upgrading the brakes???

Thanks

 

there is no sound basis to the claim that changes in tire size will induce brake failure.... Sound like massive BS to me.

But if you go to 40 series tires, up your tire pressure a few PSI and watch it like a hawk. If you don't you will wack the crap out of the rims and pinch the sidewall. Ask me how I know...

Matt

 

Ono what tire/wheels/psi where you using?
I dunno how strong rotas are...anyone know?
I think i heard that rt-615 have super strong sidewalls, why they weigh more than the compition, so hopfully that give a bit of extra safety

 

GS3ds or whatever they're called. I ended up with 36-38 psi up front cold for street driving. On the track, I'd aim for about 40-42 PSI hot.... Depending on weather, that was all over the place cold....

Matt

 

I have driven an SUV with 24" wheels, and it was a really scary experience. I was warned that the brakes didn't work so well with the four heavy flywheels (The MCS 6-sp flywheel is 26.84lbs, and those wheels definitely weighed a lot more) but couldn't believe how much worse than stock it was (yes, compared to a stock SUV). You had to plan waaay ahead like a semitruck driver. I'd consider better pads mandatory, maybe even a BBK, and not because the stock brakes look so puny in those wheels. At least perfomance tires should allow an SUV to stop faster, but that's just not going to happen if you cannot lock a wheel. Makes me wonder about those guys with the 44" tires

Then there is knowing what could happen in an avoidance maneuver, made more likely from the inability to stop.

Ford recommended 26/26psi in the Explorer (which led to the Firestones falling apart from overheating) specifically to reduce cornering traction to prevent rollovers, because as far back as 1988 it was known that the UN46 Explorer prototype would lift two wheels during violent maneuvers at 55mph when the tires were inflated to 35psi. That would have earned a "not recommended" from Consumer Reports, certainly far less acceptable than the fuel economy penalty at 26psi.

Now add "bling" ultra-low profile high performance tires... Maybe they should also warn of the risk of roof failure?

 

the brakes aren't failing... There's just more to stop.

Matt

 

Brakes are not going to fail with a tire size change.

The torque value is altered due to the diameter change however just like changing the rotor OD. It's called 'tire torque' and is not included in my bias calculator but yes changing the size does alter how much effort the tire/wheel combo applies to the road surface.

Gotta dig deeper into this for you. The changes are; smaller diameter wheels create more tq than larger ones. One inch in change nets about 5% difference. Too late today but I'll try to put some more data up tomorrow.

 

so the consensus is my ABS wont get confused and activate early and the only difference is my car will stop a little longer due to a slightly decreased longitudinal contact patch? i could always buy a tce 11.75 or 12.2 kit after my free mini brakes run out

so all I need to worry about is keeping the pressure right, I will be sure to invest in a good quality digital air gauge when I do this swap

am I correct?

thanks for the help

 

but watch the digital tire pressure guages. Most have just a half PSI resolution.. Not that good if you really are into pressure adjustments at the track. I've had a couple and now I use a mid level analog guage. I like it much better (even if it's low tech).

Matt

 

Purchase or no purchase, brand A or brand B, the ABS system only measures rotation- or lack of. You car will never know what size brakes or wheels are on it and allow you 'failure mode' of any kind. Even advanced EBD systems simply balance pressures base on the same inputs and things like pitch and yaw. The driver is still the one pushing the pedal and making pressure. The car cannot make changes unless you do that first.

 

That is exactly want I wanted to hear.

yeah because I am nuts I will do piles of research before I actually buy one (any recommendations? i know nothing about all the brands etc) hopefully soon, the one i have now is in pretty bad shape...its my dad's old one from the 80s

 

here's one manufacturer...
http://www.longacreracing.com/catalo...st.asp?catid=8
Get one with the rubber around the gauge, so that when you drop it (and you will, everyone does) it won't get destroyed.

Also note the accuracy spec (how good a reading it will make) and the resolution (how fine a measurement it can report). Nice thing about analog gauges is your brain can slice the finest reading by about a factor of 10...

Also, these numbers are independant. For example, some of the Longacre stuff has an accuracy of 0.5%, and a resolution of less than that.

Anyway, this is just one of many manufacturers. To get a real good digital, expect to pay several hundred dollars.

Matt

 

Never had a problem with 205/40/17 RA1s at the track even with Todd's BBK. FWIW These were recently driven on the street for a month - no problems.

 

http://www.longacreracing.com/articles/art.asp?artid=34

Matt

 

Brake failure is some pretty strong words. But a grain of truth is in the comment. The ABS system uses the stock sized tires at recommended pressures in its algorithms when cycling the mu slip curve. But since the MINI has 15-18 wheels, there is a decent amount of fudge room in there.

 

I'm of now help on the O/T.
My tire gauge only goes to 15psi. LOL

 

But aren't all of the overall outer diameters pretty close to each other?

thanks for the gauge tech article and tire experiences