Mazda Rotary Club

General => General Technical => Wheels & Tyres, Suspension & Brakes => Topic started by: JayD on September 11, 2012, 11:43:56 AM

Title: Thinking whether i should go 17" or 18"
Post by: JayD on September 11, 2012, 11:43:56 AM
Hi guys

currently on 18" wheels Im not sure if i want to go down or not

Can anyone with 17" wheels show me pics?

Also how do you find speed humps etc?

Thanks
Title: Thinking whether i should go 17" or 18"
Post by: wolfie1 on September 11, 2012, 08:39:36 PM
speed humps no bother at all doesnt scrape if you go over them right
17" wheels- (http://i848.photobucket.com/albums/ab48/wolfie1_bucket/DSC_0201.jpg)
Title: Thinking whether i should go 17" or 18"
Post by: JayD on September 12, 2012, 01:56:50 AM
Thanks buddy... Mine pretty low and I\'ve been caught out in London on some short humps.
Title: Thinking whether i should go 17" or 18"
Post by: m1tch on September 12, 2012, 08:31:37 AM
The question you need to be asking is: how big are my brake calipers?

15"-16" = optimal for performance with regards to acceleration (smaller rim helps with acceleration and keeps the weight down) - why do you think Mazda chose to run a fairly wide 16" on the FD?
17" = Compromise between looking good and grip performance
18"+ = show only (unless you have massive brakes fitted and need the extra clearance)
Title: Thinking whether i should go 17" or 18"
Post by: wolfie1 on September 12, 2012, 09:17:47 PM
fd also came with 17"
if you changed the aspect ratios of the different sized tyres you would be able to have the same rolling circumference!
for example a 205/60 16 would have the same rolling circumference as a 235/35 18, if you go onto michelins website there is a guide there to the exact figures
Title: Thinking whether i should go 17" or 18"
Post by: m1tch on September 12, 2012, 10:30:40 PM
Quote from: wolfie1;835675fd also came with 17"
if you changed the aspect ratios of the different sized tyres you would be able to have the same rolling circumference!
for example a 205/60 16 would have the same rolling circumference as a 235/35 18, if you go onto michelins website there is a guide there to the exact figures

Wasn\'t that due to them running larger disks on some models though?
Title: Thinking whether i should go 17" or 18"
Post by: wolfie1 on September 13, 2012, 06:41:07 PM
dont know, could have been, makes sense
Title: Thinking whether i should go 17" or 18"
Post by: JayD on September 13, 2012, 08:56:38 PM
Quote from: wolfie1;835675fd also came with 17"
if you changed the aspect ratios of the different sized tyres you would be able to have the same rolling circumference!
for example a 205/60 16 would have the same rolling circumference as a 235/35 18, if you go onto michelins website there is a guide there to the exact figures

That\'s very interesting ummm...

What size tires do you run on your 17"?
Title: Thinking whether i should go 17" or 18"
Post by: wolfie1 on September 13, 2012, 09:08:04 PM
225/45 17 on the front and 255/40 17 on the rear
Title: Thinking whether i should go 17" or 18"
Post by: JayD on September 14, 2012, 02:25:41 AM
Umm tempting... i would like to run 9.5" or 10" on the rear
Title: Thinking whether i should go 17" or 18"
Post by: RotRex on September 14, 2012, 06:02:56 PM
Quote from: wolfie1;835743225/45 17 on the front and 255/40 17 on the rear

Why the lower profile at the rear? Should it not be the other way for high speed stability or have you compensated with adjustable suspension?
Title: Thinking whether i should go 17" or 18"
Post by: m1tch on September 14, 2012, 07:11:12 PM
Quote from: RotRex;835807Why the lower profile at the rear? Should it not be the other way for high speed stability or have you compensated with adjustable suspension?

The \'lower profile\' is due to the wider tyre, the profile of the tyre is the % of the tyre width so having a wider tyre will mean a lower profile as its done as a % to match the same circumference so both tyres are basically the same:

225/45/17 vs 255/40/17 = 6mm difference in circumference
225/45/17 vs 255/45/17 = 88mm difference in circumference

http://www.alloywheels.com/Tyre_Calculator
Title: Thinking whether i should go 17" or 18"
Post by: RotRex on September 14, 2012, 08:57:43 PM
Quote from: m1tch;835813The \'lower profile\' is due to the wider tyre, the profile of the tyre is the % of the tyre width so having a wider tyre will mean a lower profile as its done as a % to match the same circumference so both tyres are basically the same:

225/45/17 vs 255/40/17 = 6mm difference in circumference
225/45/17 vs 255/45/17 = 88mm difference in circumference

http://www.alloywheels.com/Tyre_Calculator

Interesting. It potentially opens up a range of tyre choices. I will have to use the calculators next time I get tyres. Or ask you for advice.
Title: Thinking whether i should go 17" or 18"
Post by: wolfie1 on September 14, 2012, 09:41:20 PM
just realised a typo i made, i am running 235/45 17 on the front
Title: Thinking whether i should go 17" or 18"
Post by: kummbho on December 01, 2012, 06:35:19 AM
fd also came with 17"
if you modified the element percentages of the different scaled car tyres you would be able to have the same moving circumference!
for example a 205/60 16 would have the same moving area as a 235/35 18, if you go onto michelins web page there is a information there to the actual figures
Title: Thinking whether i should go 17" or 18"
Post by: Grant Monkhouse on December 08, 2012, 10:52:40 AM
Quote from: m1tch;835595The question you need to be asking is: how big are my brake calipers?

15"-16" = optimal for performance with regards to acceleration (smaller rim helps with acceleration and keeps the weight down) - why do you think Mazda chose to run a fairly wide 16" on the FD?
17" = Compromise between looking good and grip performance
18"+ = show only (unless you have massive brakes fitted and need the extra clearance)

This isn\'t exactly true, you can keep the overall circumference of the wheel tyre combo on an 18" rim the same as a 16" rim tyre combo. You have to choose the the correct size profile, different widths also effect the overall size of the tyre so if you have a 235 on the front wheels and a 265 on the rear the profiles have to be different to achieve the same overall size.

The new GTR runs 20" rims iirc and that goes around corners better than any rotary.

However if I was racing a car I would go with 17" wheels and a good tyre combo to keep the overall size as close to the original FD sizes. Plus the costs of the tyres is less
Title: Thinking whether i should go 17" or 18"
Post by: Grizzly on December 08, 2012, 11:59:05 AM
Quote from: Grant Monkhouse;844023The new GTR runs 20" rims iirc and that goes around corners better than any rotary.


Wo wo wo Cowboy, Sorry did i read this right :)
Title: Thinking whether i should go 17" or 18"
Post by: Grizzly on December 08, 2012, 12:03:50 PM
Quote from: m1tch;83559515"-16" = optimal for performance with regards to acceleration (smaller rim helps with acceleration and keeps the weight down) - why do you think Mazda chose to run a fairly wide 16" on the FD?
17" = Compromise between looking good and grip performance
18"+ = show only (unless you have massive brakes fitted and need the extra clearance)
All about Unsprung weight, Don\'t forget the stock FD rims and Tyres don\'t weigh allot at all so to keep good performance it don\'t matter if there 15-19" as long as you don\'t add any more weight. There is a task for you right there ;)

If you can keep the Rim/tyre weight the same then all you are doing by going between 17-19" is reducing the side wall so there is less tyre distorsion through corners.

Imho about 24" arch to floor and 24 1/4 at the rear then put what ever wheel combo you want on that keeps it there (shouldn\'t matter what Rim size you pick as you drop the side wall to compensate)
Title: Thinking whether i should go 17" or 18"
Post by: Grizzly on December 08, 2012, 12:38:48 PM
Remember the middle number 225/45/17 (45) is a Percentage of the width (225) so 45% of 225 is approx 100, so you need to keep that about the same for the rear (or as close as) so 245/4017 would be 98 and 255/40/17 would be 102. So ether would work together without looking daft. If you didn\'t drop the % so you had 225/45/17 and 255/45/17 rear the Rears would be 15mmx2 (30mm) fatter side wall hence the reason you drop the Aspect ratio (% of the width of the tyre)
Title: Thinking whether i should go 17" or 18"
Post by: Grant Monkhouse on December 08, 2012, 12:41:23 PM
Quote from: Grizzly;844026Wo wo wo Cowboy, Sorry did i read this right :)

The 787B doesn\'t count
Title: Thinking whether i should go 17" or 18"
Post by: Grizzly on December 15, 2012, 10:51:58 AM
Bone stock maybe but Places like Revolution and ReA might have some thing to sat about that :)


http://www.youtube.com/watch?v=Kd-AnG3LYUg in fact its so fast they put a TV in so the Driver has something to do once he\'s spanked them all and Cruising :D
Title: Thinking whether i should go 17" or 18"
Post by: Grizzly on December 15, 2012, 11:29:50 AM
Quote from: Grant Monkhouse;844023The new GTR runs 20" rims iirc and that goes around corners better than any rotary.

All the new Tech in the world can\'t beat Gravity :) The FD has a Very Low COG and 1260kg, the GTR does have a Low COG but not in the same ball park and it has 1700kg to deal with, its why the GTR still struggles to beat the FD on the Touge etc when it comes down to Handling and can\'t be covered up with Power. ;)