GBW Posted December 16, 2008 Report Share Posted December 16, 2008 (edited) Hi all. Just wondering something about wheel size and the speed'o. I have 205/55R16 wheels on my Subaru and my brother in law has given me his winter set as he no longer has that car. They are also the same bolt pattern as mine (came off a Toyota so they could fit?) but they are 206/65R15's. If i can get them to fit properly, does anyone know how much this will change my speedometer? Thanks. Geoff Edited December 16, 2008 by GBW Link to comment Share on other sites More sharing options...
irishfield Posted December 16, 2008 Report Share Posted December 16, 2008 Take a sewing tape measure and measure the tire circumference. Divide original tires circumf by the snows to get the correction multiplier. If the new ones are smaller... when the speedo reads say 80KPH divide by the correction number...speed will be slower than the reading because the speedo is reading the output shaft of the transmission RPM... and the smaller tires aren't taking you as far as it thinks it is. Link to comment Share on other sites More sharing options...
Bass_boy7 Posted December 16, 2008 Report Share Posted December 16, 2008 basically you will be putting less kms on your vehicle so don't worry about it, its winter rims be safe drive safe, and enjoy your vehicle. Link to comment Share on other sites More sharing options...
Bernie Posted December 16, 2008 Report Share Posted December 16, 2008 (edited) First problem will be the wheels. I highly doubt they will fit. There are several factors involved. First is the bolt pattern and distance between the holes. Some have different fastener design ( tapered nut vs flat). Also will the inner part of the wheel clear the calipers and any other parts that fit very snug inside wheels in modern cars. Also have seen where air flow to keep brake components cool has been an issue. Also antilock brakes become a possible problem when wheel speed, diameter and programmed ABS all come into play. Be very cautious about doing this. Edited December 16, 2008 by Bernie Link to comment Share on other sites More sharing options...
GBW Posted December 16, 2008 Author Report Share Posted December 16, 2008 I just decided to go out and have a look and see if there is a diff. in the total diameter and yes there is. It's almost one inch, larger. So, if I get these to fit properly and my speed'o is reading 100KPH what will I be actually doing? Thanks again. Link to comment Share on other sites More sharing options...
irishfield Posted December 16, 2008 Report Share Posted December 16, 2008 (edited) basically you will be putting less kms on your vehicle so don't worry about it, its winter rims be safe drive safe, and enjoy your vehicle. If the snows are smaller... he will be putting more "miles" on his car odometer...than he's really going. Since his speedo will read higher than the speed he's really doing. GBW... do the math I set out above. Remember you are measuring the circumference around the tread.. not the diameter. Edited December 16, 2008 by irishfield Link to comment Share on other sites More sharing options...
Bernie Posted December 16, 2008 Report Share Posted December 16, 2008 (edited) Pie X radius squared x distance of each tire then figure the difference. But it won't matter. Be more concerned about the wheels first. You are going to a smaller diameter wheel. It probably wont fit over your caliper even if the bolt holes are the same. Edited December 16, 2008 by Bernie Link to comment Share on other sites More sharing options...
GBW Posted December 16, 2008 Author Report Share Posted December 16, 2008 ok, so because these are about 1" larger in the total diameter I'll be going faster then the reading on the dash. Bernie, thanks. I do have both set's (tapered nut vs flat) as my bro-in-law gave them to me. The ones I have from my car and the one's from the Toyota. I would guess that with both being Japanese made cars maybe they cut some costs by using the same rotors spec's from time to time... I did check the depth of the wheel on both (on the car and the new ones) and both run at 6" of space from the back where the wheel meets the spindle and the edge of the wheel so the wheel sticking out or tucked in should not be an issue. The gap around the calipers looks to be a decent gap. I guess to tell that I have to take a wheel off and try one of the new ones to know for sure. My concern was the speed'o as i can buy new wheels and put these tires on them... Thanks again all. Link to comment Share on other sites More sharing options...
GBW Posted December 16, 2008 Author Report Share Posted December 16, 2008 BTW, my spare is a 14" wheel so I gather if the bolt pattern is a fit I may be ok? Link to comment Share on other sites More sharing options...
Cudz Posted December 16, 2008 Report Share Posted December 16, 2008 (edited) Pie X radius squared x distance of each tire then figure the difference. But it won't matter. Be more concerned about the wheels first. You are going to a smaller diameter wheel. It probably wont fit over your caliper even if the bolt holes are the same. They could fit over the calipers. Generally speaking you can go down one inch on the rim size and have no issues with calipers unless you have upgraded multi-piston or aftermarket products. Might want to look at the offset as well but that is less imprtant especially on winters.. My car runs 16" wheels in the summer and 15s in the winter. do this calculation to fisn out the overall difference in diameter of the 2 sets of wheels. Summer tires 2(205 x .55) + 400 = 625.5 mm which is almost exactly 25 inches. Therefore your tires stand 25" tall Winter tires 2(205 x .65) + 375 = 641.5 mm which is about 25.66". Therefore your winter tires would be 25.66" tall I believe the recommended allowance is about 1 cm or 10 mm. Your difference is 16 mm or 1.6 cm. Not too bad. Your speedo will be off a bit but not all that much. Your tires will be about 2.6% taller than the originals. Edited December 16, 2008 by Cudz Link to comment Share on other sites More sharing options...
GBW Posted December 16, 2008 Author Report Share Posted December 16, 2008 Thanks for the math results "teach"!!! (no joke, I mean it) Well, thanks to all that posted to help me out!! Now it's time to try and find time to take one Subaru wheel off and test the Toyota's that I now have from my bro-in-law. Not tonight... maybe if I find time this weekend... Link to comment Share on other sites More sharing options...
GBW Posted December 16, 2008 Author Report Share Posted December 16, 2008 Cudz, you did say before that you teach right? Link to comment Share on other sites More sharing options...
Cudz Posted December 16, 2008 Report Share Posted December 16, 2008 Cudz, you did say before that you teach right? LOL. Yes I do. It is now 12:48 am and I had better get to bed. I have to be more awake than the kids tomorrow. Link to comment Share on other sites More sharing options...
GBW Posted December 16, 2008 Author Report Share Posted December 16, 2008 LOL. Yes I do. It is now 12:48 am and I had better get to bed. I have to be more awake than the kids tomorrow. HAHA, that's not why I asked. Check your PM. Link to comment Share on other sites More sharing options...
Raf Posted December 16, 2008 Report Share Posted December 16, 2008 (edited) the 15" wheels should fit over your brakes provided you haven't upgraded them or you drive an STi. double check the spacing. http://www.miata.net/garage/tirecalc.html ^ great tire size calculator ^ be aware that your spare will be a different diameter - not particularly good for awd vehicles. Edited December 16, 2008 by Raf Link to comment Share on other sites More sharing options...
GBW Posted December 16, 2008 Author Report Share Posted December 16, 2008 Thanks Raf! Link to comment Share on other sites More sharing options...
douG Posted December 16, 2008 Report Share Posted December 16, 2008 Your speedometer will read about 2.49 % too slow, off the top of my head, I'm pretty much certain. Link to comment Share on other sites More sharing options...
Raf Posted December 16, 2008 Report Share Posted December 16, 2008 which should just about even things out - i've noticed that speedos in cars usually read a bit high. Link to comment Share on other sites More sharing options...
Cudz Posted December 16, 2008 Report Share Posted December 16, 2008 which should just about even things out - i've noticed that speedos in cars usually read a bit high. I have read that some are as bad as 10% at slower speeds. Link to comment Share on other sites More sharing options...
Kirk Posted December 16, 2008 Report Share Posted December 16, 2008 (edited) Since the wrong tire size is probably being used...you will pick up lots of free km with skidding and sliding distance with your wheels locked not showing up on speedometer (sliding on the roof of your car = more free km, scrapes will buff out) Edited December 16, 2008 by Kirk Link to comment Share on other sites More sharing options...
Raf Posted December 16, 2008 Report Share Posted December 16, 2008 huh? i guess all the jeep owners running oversized tires are spending lots of time on their roofs? Link to comment Share on other sites More sharing options...
Kirk Posted December 16, 2008 Report Share Posted December 16, 2008 call me old school, I stick to the tire size in the manual...don't use other sizes...Jeeps and 4x4 with 'oversize tires' must be for riding the ditches on the 404 and 400...thats where they all go in winter. Great for tow truck drivers LOL and I will admit that they are not on their roofs, so we can give them credit for that. Link to comment Share on other sites More sharing options...
Raf Posted December 16, 2008 Report Share Posted December 16, 2008 live a little! Link to comment Share on other sites More sharing options...
Cudz Posted December 16, 2008 Report Share Posted December 16, 2008 I used to run 33" on a grand cherokee. I also ran 235 70 16 for 3 years on a vehicle that was supposed to have 225 70 16. People make too big an issue with the exact size. Lawsuits blah blah. When I lived in the Dubai I ran 245 70 16 on my range rover that was supposed to have 205 80 16. Wider footprint and bigger sidewall for the sand. WIth a bigger sidewall I could lower tire pressure and get a much bigger footprint with each tire on the sand. I don't recommend different front to rear or side to size tires at the same time but people are a bit too caught up with this exact size thing. I had a Jetta that had 3 different sizes recommended in the manual. Their overall diameters were considerably different as well. Link to comment Share on other sites More sharing options...
GBW Posted December 16, 2008 Author Report Share Posted December 16, 2008 Since the wrong tire size is probably being used...you will pick up lots of free km with skidding and sliding distance with your wheels locked not showing up on speedometer (sliding on the roof of your car = more free km, scrapes will buff out) did I say I was a crazy driver? More concerned about the fit, being safe and not needing to answer the question from the OPP saying "do you know how fast you were going?" huh? What I was thinking too when I first read the post. I don't recommend different front to rear or side to size tires at the same time but people are a bit too caught up with this exact size thing. I had a Jetta that had 3 different sizes recommended in the manual. Their overall diameters were considerably different as well. That's it, time for me to RTM and see what is listed. Thanks! Link to comment Share on other sites More sharing options...
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