Bigger rear tire-Venture Diif?

[BothaBoeta]

So I'd like to put a larger rear tire on my 97 Max.Do the RPM's go up if the rear tire is larger?I searched the Forum and saw a post on using the Venture Diff to bring down the RPM's?

If the rev's do go up,will I only need the Venture diff,or are there other little things I need to consider?
Also I read a 170 will fit without modifications,and someone even said a 190 will.Will the 170 fit on my standard rim?
Thank you in advance
Philip

 

[Redbone]

With a larger circumference tire the tire rotation is slower so the tire will travel farther in one rotation than a tire of smaller circumference.
So no, your engine rpms will not go up if you use a larger diameter tire.
Here is some more info on the subject: http://www.csgnetwork.com/tiresizescalc.html

 

[Rollie]

With a larger circumference tire the tire rotation is slower so the tire will travel farther in one rotation than a tire of smaller circumference.
So no, your engine rpms will not go up if you use a larger diameter tire.
Here is some more info on the subject: http://www.csgnetwork.com/tiresizescalc.html

Acceleration will pick up noticeably . unk:

 

[KJShover]

I read a 170 will fit without modifications,and someone even said a 190 will.Will the 170 fit on my standard rim?
Thank you in advance
Philip

The 170 will fit nicely on the stock rim. you can shoehorn in a 180-190, but it will be deformed and screw up your steering if you use the stock rim. best to go with a 5.5" rim if you want a 180-190.

 

[[email protected]]

Larger diameter, I.e. taller tire equals less rpm, less acceleration, more top end speed. Smaller diameter or shorter is just the opposite.

Width will make no difference in any of those factors

 

[RaWarrior]

It's the other way round, you'd lose acceleration.

A Venture drive is geared higher than the stock. I'm sure someone knows the ratio, but effectively you'll spin about 400RPM less on the highway to go the same speed. So your acceleration will suffer slightly, with the trade off of better fuel economy, and higher theoretical top speed. For me, 75mph in fifth, with a Venture drive is around 4400 RPM. In theory, my bike could go 161mph at redline, in reality it's around 145-150@88-8900RPM. Which is about what a stock bike will do at redline, so in practice you don't really gain any top end since the motor just don't have any more power to give(assuming it's stock or nearly so).

A 170 tire is not any larger than the stock 150, it's wider. The circumference should be nearly identical, so your effective gearing would be unchanged. A 170 will fit no problem.

170/80-15 translates to 170mm wide/80% as tall(profile) as it is wide- 15" rim

 

[Rollie]

brain fart ( still ecstatic about the Falcons ) , was thinking of 15 " vs. 17" wheels. :confused2:

 

[vmaxcruzer]

If you're gonna do it right, you should invest in a widened rim for a 17" or 18" radial and keep the stock rear. Ive had all the combo's were talking about here at one time or another and if its a look or performance you're after at the tire, widening is way better. Raising your final drive is negligible. I saw more of a difference in power loss than gas savings and eventually put my stock one back on. Can't remember the ratio but the difference between the two is one tooth. It wasn't a slug by any means with the venture, but saving gas didn't out weigh the giddy-up. I have the stock rear shocks and the front lowered 1" and my bike sits level with a 17".

 

[RaWarrior]

I have heard that a 17" radial rear and the Venture drive effectively puts things about back to stock. The Venture pumpkin raises the ratio a bit, and the smaller wheel lowers it back down, it about balances out.

I never ran the stock diff so I can't personally compare, but it seems like I get better mileage/range than most here, easily 115-120 to the fuel light. The bike is still an animal, and lights up the rear 170 no issue, it'll even still pick the front end up. I don't race or drag or anything, so I don't really care if the 0-60 is now .1 seconds slower. If you do, then stick with the stock.

 

[vmaxcruzer]

I suppose with a 17" effectively raising RPM (X amount) because its smaller in diameter, you could off set that with a venture and settle somewhere close to stock. Don't forget to factor in the extra weight of the rim, if you widen it...DAMN! More math.:biglaugh:

 

[88vmx12]

I want to chime in! Ok I have been told that if you go to a 18"wheel the tire overall diameter is almost the same as stock. Now let's say that you have an 18" wheel and then go to an Venture final drive. Since the gear ratio is "taller" then sure your RPMs will drop but....... you will also lose some torque and in theory your bike will have better fuel economy. Now If you have a 17" wheel and tire combo the tire {190/50/17} is shorter in height than a stock tire by about 1/2". Now with this your RPMs are going to go up when traveling at the same speed across the board VS the other set up. Also you will gain some torque. But your fuel economy goes down. So to cure this issue with the 17" and get the RPMs back down and the fuel econmy back up to what stock would be. You install a Venture final drive. The 17" widened stock wheel, 190/50/17 tire and the Venture final drive is what I have. Now the tire is in a notched, extended swingarm and yes they do fit! provided you get the correct brand! Not all brands are the exact same....
G

 

[vmaxcruzer]

I learned that too, after I had my 17" for a while. I wonder what the 18" tire ratio would be like with both rears. I also recall a looong thread arguing the extra weight and rim mass...Blah blah blah.
The real question is, how much money does Philip have?

 

[Redbone]

OR...you could go with a OD 5th gear and have the first 4 gears for playing then OD 5th for economy.
Maybe a 17" tire, venture diff, and OD 5th is a good combo???:ummm:

 

[BothaBoeta]

"I learned that too, after I had my 17" for a while. I wonder what the 18" tire ratio would be like with both rears. I also recall a looong thread arguing the extra weight and rim mass...Blah blah blah.
The real question is, how much money does Philip have?"

I have no money,if anyone has some leftover money please send it my way...! thanks for all the input.As soon as my nagging wife lets me,I'm sticking on a 170,and being the ninny I am I'll stick in a Venture diff to keep the Rpms down on the highway...

 

[one2dmax]

Stock Vmax Ratio is 3.66 vs the Venture Ratio of 3.33. That's approx 10% change in rpm.

Sean

 

[95spfldmax]

A 170 tire is not any larger than the stock 150, it's wider. The circumference should be nearly identical, so your effective gearing would be unchanged. A 170 will fit no problem.

When I went up in size at both ends (150 to 170 rear & 110 to 120 front) I lost 5MPH per 5k RPM. Bike now does 75MPH @ 5k RPM but used to do 80MPH.

 

[Redbone]

When I went up in size at both ends (150 to 170 rear & 110 to 120 front) I lost 5MPH per 5k RPM. Bike now does 75MPH @ 5k RPM but used to do 80MPH.

That's as it should be Mike, according to the calculator. See link, but a comparative calculation whereas all dimensions are the same with just the width changed from 110 to 120 results in a drop of 2.14 mph at 80 mph (80 mph vs. 77.86).
http://www.csgnetwork.com/tireinfo4calc.html

 

[vmaxcruzer]

Lets start a collection for Philip.:clapping:

 

[RaWarrior]

That's as it should be Mike, according to the calculator. See link, but a comparative calculation whereas all dimensions are the same with just the width changed from 110 to 120 results in a drop of 2.14 mph at 80 mph (80 mph vs. 77.86).
http://www.csgnetwork.com/tireinfo4calc.html

Ah, but that's on the front wheel, where the speedo reads from, not where motion comes from. The perceived difference is from speedometer error, since it's no longer calibrated right.

Using the same calculator, the switch from a 150/90 to 170/80 results in a .2" bigger circumference (80.5 to a 80.7"), or less than .3% change. At the same wheel speed, if the 150 was doing 80mph, at the same rotational speed, the 170 would be doing 79.8. Negligible in my book

The 120 front is more significantly larger in circumference, and thus turns a bit slower at the same speed, so the speedometer reads slower. Your actual speed/RPMs are unchanged.

I kept the stock 110 front and put a 170 on the back and noticed no change, the front wheel is throwing off your speedo, the back makes essentially no difference at all.

 

[Redbone]

Ah, but that's on the front wheel, where the speedo reads from, not where motion comes from. The perceived difference is from speedometer error, since it's no longer calibrated right.

Using the same calculator, the switch from a 150/90 to 170/80 results in a .2" bigger circumference (80.5 to a 80.7"), or less than .3% change. At the same wheel speed, if the 150 was doing 80mph, at the same rotational speed, the 170 would be doing 79.8. Negligible in my book

The 120 front is more significantly larger in circumference, and thus turns a bit slower at the same speed, so the speedometer reads slower. Your actual speed/RPMs are unchanged.

I kept the stock 110 front and put a 170 on the back and noticed no change, the front wheel is throwing off your speedo, the back makes essentially no difference at all.

I did the calculations on the stock front tire (110/90-18) Vs. wider front tire (120/90-18) since the rear makes no difference in measuring speed on a stock Vmax and it's speedometer. I'm not sure what the exact tire sizes that Mike was working with so I kept the tire size/ aspect ratio the same then used the widths of 110 and 120 for a example of the possible speed differences. I provided the link so he could put in different sizes so he could see his exact results.:clapping: