Rad City Chainring advice to increase top speed! Help Please!

Jim Mass

New Member
Sierra. I tried your calculator with the following chain ring sizes.
Results: 46 T on 11 gear = 108.5; 42T on 11T gear = 99.0 and 52 T on 11 gear = 122.6

I don't care that much about top speed. Would I like to get up to 25 mph? sure...Though at age 76 riding in a t shirt and bike pants don't want to fall off it at that speed. More so peddle resistance. Which chain ring would increase peddle resistance?
 

Sierratim

Well-Known Member
Sierra. I tried your calculator with the following chain ring sizes.
Results: 46 T on 11 gear = 108.5; 42T on 11T gear = 99.0 and 52 T on 11 gear = 122.6

I don't care that much about top speed. Would I like to get up to 25 mph? sure...Though at age 76 riding in a t shirt and bike pants don't want to fall off it at that speed. More so peddle resistance. Which chain ring would increase peddle resistance?
Jim,

Looks like you selected "gear inches" for this calculator's "Gear units"? I find it easier to discuss peddling 'spin out' as the OP implied when selecting a cadence/rpm value. With that said, this calculator won't estimate the rider's effort. Other calculators do this, though they need to know much more about the motor output. Grin Technologies has a popular calculator that will help with this.

So, which chainring will increase pedal resistance? The simple answer is any chainring with a tooth count higher than you have now. Not helpful, I know but in knowing your comfortable cadence range and motor electrical characteristics you can use available online calculators to get this data.

Maybe what you really want is to avoid 'spin out' under your riding conditions? The calculator at sheldonbrown.com can help with this using rpm as "Gear units".
 

EBJ

Member
...My complaint is lack of "pedal resistance" over 21 mph. Reason I only use PAS 4&5 in really steep hills. Feels like I need another lower gear. So I'm researching chain rings. Has anyone tried or can one even buy a chain ring 36-38 T?

I think you've got this completely backwards. If you want to avoid spinning out/add pedal resistance in 6th or 7th gear, you need a front chainring with more teeth, not less.
 

Jim Mass

New Member
Hmm Sierra, Not sure I understand everything you said. What does "spin out" mean? Back 3 years ago before buying the electric bike I had a 24 speed cross-over bike. 3 gears in the front and a 8 gear cassette in the rear. Mostly I rode it in 16th-17th range and always had pedal resistance. If it got to be too much I would down shift.

I know I can't compare the bikes because there is a lot of difference between the 63 pound ebike and the regular 30 pound cross-over.

I ride the RAD step thru in PAS 1 (what I call exercise mode) in 7th gear at about 15-18mph and have plenty of pedal resistance 95% of the time. I get a hill I use the throttle. When I am on the street (25 mph posted) I ride PAS 3 -7th to keep up with traffic. No resistance so I use a lot of throttle to maintain 23 mph. In inclines of 3-4% I'm in PAS 3-4 in 4th -5th gear with plenty of resistance. Highest hill I've ever climbed was 6% grade in PAS 5, gear 1 - going 1 mph with lots of resistance. I crested the hill sitting down. Proud of myself, Don't plan on doing that again.

Maybe how I'm riding on the flat 95% of the time for exercise is all the RAD City is capable of for the money I paid. If I want more I will have to upgrade to a $4K bike. At my age not worth it.

One last thing. I finally upgraded the seat post to a "Thunderbuster ST G4." Best decision I ever made. My butt is very happy now. 25 miles now feels like 18 instead of 35.
 

Jim Mass

New Member
I think you've got this completely backwards. If you want to avoid spinning out/add pedal resistance in 6th or 7th gear, you need a front chainring with more teeth, not less.


Thanks EB I think you answered my question. There is a 52T chain ring I saw online that based on Sierra's formula has a final ratio of gear #7 somewhere around 122.6 as I inputted the other numbers. Wheel diameter - Tire size 26 x 2.125, 170 mm crank, Shimano 11-34 T - speed "mega-Range Freewheel, . The 46 T 108.5 on Gear # 7 should be more resistance...maybe??
 

BKing

Member
Jim, you mentioned needing a lower gear when in PAS 4 and 5 up hills. You also mentioned needing a higher gear for down hills to maintain pedal resistance. I assume you have a 2020 City. You just need the 46 tooth front chain ring for the down hill problem. But this will also make it harder to go up hills if you are in gear 1 and PAS 4 or 5 and already having trouble going up. There is a limit on these bikes for uphill performance unless you are really light. You probably can’t fix both problems so go ahead and fix the down hill issue. Everyone is different on pedaling speed, what one rider thinks is pedaling too fast is just right for a rider that knows about perfect efficiency which is faster pedaling than 90 percent of riders you see on the road. I would not go higher than a 46 tooth in hilly country. For heavier riders like me, we don’t need to pedal much going down steep hills, the total weight takes off like a rocket. I have hit 34 mph with no pedaling after 25.
 
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Geno929

Member
I think you've got this completely backwards. If you want to avoid spinning out/add pedal resistance in 6th or 7th gear, you need a front chainring with more teeth, not less.
That is exactly what I made this post about. The stock 42 tooth chainring, that used to be 46 tooth, is not allowing me to spin in 6th or 7th gear.
 

EBJ

Member
It appears Geno has had a good grasp on the situation from the beginning and has been pursuing a reasonable solution in terms of his personal preferences if he can find a chainring with the correct BCD for the City with a couple of extra teeth. He may or may not need a new (longer) chain, and the chain MAY not stick up above the chainring bash guards enough to require replacement with new larger guards (might be tough to find something compatible with the crank arm), or use a pant leg strap/clip.

Jim on the other hand has been all over the place, and if he now wants to go to something like a 53 tooth chainring, he will almost certainly need a longer chain and the stock chainring bash guards will be way too low to do what they were intended.
 

Geno929

Member
It appears Geno has had a good grasp on the situation from the beginning and has been pursuing a reasonable solution in terms of his personal preferences if he can find a chainring with the correct BCD for the City with a couple of extra teeth. He may or may not need a new (longer) chain, and the chain MAY not stick up above the chainring bash guards enough to require replacement with new larger guards (might be tough to find something compatible with the crank arm), or use a pant leg strap/clip.

Jim on the other hand has been all over the place, and if he now wants to go to something like a 53 tooth chainring, he will almost certainly need a longer chain and the stock chainring bash guards will be way too low to do what they were intended.
Thanks EBJ for the advice. I did order a 130 BCD 44 tooth chainring, but it was smaller (outside diameter) than the current 130 BCD 42 tooth chainring on my Rad City. I've been looking for a 130 BCD 44 or 46 tooth chainring that will allow me to pedal at a slower cadence (80 - 95 rpm) and maintain current speed. Gosh, I'm starting to sound like a punter! Have a great day!
 

Sierratim

Well-Known Member
Hmm Sierra, Not sure I understand everything you said. What does "spin out" mean?
"Spinning out" refers to pedaling as fast as you can (max cadence) yet wanting to go faster. The rider has reached the maximum speed they could in the gears they have. The implication is that with a bigger gear they could have gone faster in the same scenario.

It sounds like you're 'spinning out' at 23mph. A larger chainring would help with this, but as @BKing notes this will negatively impact hill climbing ability.
 
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Sierratim

Well-Known Member
Thanks EBJ for the advice. I did order a 130 BCD 44 tooth chainring, but it was smaller (outside diameter) than the current 130 BCD 42 tooth chainring on my Rad City. I've been looking for a 130 BCD 44 or 46 tooth chainring that will allow me to pedal at a slower cadence (80 - 95 rpm) and maintain current speed. Gosh, I'm starting to sound like a punter! Have a great day!
So the crank bolts are correctly placed at 130BCD?

If the new 44t chainring was smaller in diameter than what you have you must have a ring with more teeth since the teeth are all spaced the same. I'd suggest verifying your tooth count before reordering.
 

Jim Mass

New Member
Jim, you mentioned needing a lower gear when in PAS 4 and 5 up hills. You also mentioned needing a higher gear for down hills to maintain pedal resistance. I assume you have a 2020 City. You just need the 46 tooth front chain ring for the down hill problem. But this will also make it harder to go up hills if you are in gear 1 and PAS 4 or 5 and already having trouble going up. There is a limit on these bikes for uphill performance unless you are really light. You probably can’t fix both problems so go ahead and fix the down hill issue. Everyone is different on pedaling speed, what one rider thinks is pedaling too fast is just right for a rider that knows about perfect efficiency which is faster pedaling than 90 percent of riders you see on the road. I would not go higher than a 46 tooth in hilly country. For heavier riders like me, we don’t need to pedal much going down steep hills, the total weight takes off like a rocket. I have hit 34 mph with no pedaling after 25.

Thanks for your response BKing. I have the 2018 City with the 46T crankset. I ride 95% on the flat for exercise. We have a 9 mile asphalt trail about a block away from cars that parallels a river. The city built it on top of the levy. that goes under all major streets and terminates near the Oceanside Marina in San Diego county.( we ride around the marina or surface streets that paralel the ocean than ride back up the trail to the trail head). It passes a large park with clean bathrooms about 8 miles east of the marina. Wonderful safe area to ride on. In PAS1 gear #7 or #6 (headwind) I can maintain 15-18mph. Going down under the major streets the up portion is very steep for maybe 150 feet. I stay in 7th, keep pedaling with lots of throttle easily climbing the short 4-6% grade reaching the top at 8-10 mph. Then I'm back on the flat with lots of pedal feel unless I downshift to build my momentum back up.

I cruise on the local 25 mph marked rodes In PAS 3 sharing the rode with the cars (no marked bike lane). PAS 3 keeps me up around 22 mph so I don't feel intimidated by the cars. They are surprised at how much speed I can maintain and how fast off the line that I am. Like you I coast down the hills and its nice to know how fast it goes . The neighborhood I live in very hilly. One hill named "Cardiac" by the walkers is a long 4-5% grade (8 long blocks). Starting at the bottom dead stop in PAS 3 gear # 4 I'm doing 15 - 18 mpg at the top. The bike easily handles the various hills in PAS 3 or 4 downshifting to # 4 or # 5 gear. I just stay out of PAS 4 & 5 on the flats as there is no speed increase. I figured out by trial and error those PAS numbers are just for going up hills.

I decided for now to not change out the chain ring because I don't know the consequences of doing so.
 

BKing

Member
Good idea, I think it’s just the 2020 City that needs a 46 tooth unless someone needs more help getting up hills then just leave it stock. Sounds like you are having a blast the way it is! I don’t want mine to go any faster due to the kids around here that ride their bikes on the wrong side of the neighborhood streets and constantly turn their heads to look behind them. When they do that, their bike veers off track drastically. We also have 14 year old kids driving golf carts the wrong way in traffic circles. I never take my fingers off the brake levers.
 

ExPatBrit

Active Member
I went with 3 inch tires on my Rover for the summer, I removed the stock 42T and installed a 46T to compensate for the lower circumference of the tire/ wheel combo.

I commute to work on my bike, It does make it more usable at the high end, 5th gear is more like 7th gear used to be .

I can pedal up to about 28 mph on the flat before my legs can't keep up.
 

Jim Mass

New Member
That is reason i wondered if I switched from a 46 T to a 52 T if my 5th gear would be like my 7th and I would have two more gears
 

BKing

Member
I went with 3 inch tires on my Rover for the summer, I removed the stock 42T and installed a 46T to compensate for the lower circumference of the tire/ wheel combo.

I commute to work on my bike, It does make it more usable at the high end, 5th gear is more like 7th gear used to be .

I can pedal up to about 28 mph on the flat before my legs can't keep up.

So the 4 teeth made quite a bit more difference than changing the tire size.
Did you program in the effect of the tire size change or does it have enough choices. Use a gps app on your phone for accurate mph if you can safely look at it while going fast. I don’t think a Rad can go 28 on flat ground with 46 teeth unless you are a high end athlete standing up pedaling.
 
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Jim Mass

New Member
BKing. Good point about losing 1st and 2nd. In my case not an issue as I never except that one time ever been below 4th gear. The City is not a mountain bike. A City bike is used mostly flat (except if your in San Francisco then maybe one does need a 42T). The road bike guy I passed in PAS 2 gear # 7 easily re-passed me as he up shifted to his last higher gear. He had skinny 29 " tires. Bike weighed 22 pounds. He pulled away like he had a rocket engine behind him. I think I passed him because he was getting tired and his metal seat hurt his butt. While I was riding in luxury with my Thunderbuster suspension seat post, soft seat, and 63 pound frame with only 60 pounds in the tires. I love "cheater bikes" especially at my age.
 

ExPatBrit

Active Member
So the 4 teeth made quite a bit more difference than changing the tire size.
Did you program in the effect of the tire size change or does it have enough choices. Use a gps app on your phone for accurate mph if you can safely look at it while going fast. I don’t think a Rad can go 28 on flat ground with 46 teeth unless you are a high end athlete standing up pedaling.

I didn't check it with a GPS but it matches the speed monitoring / warning radar sensors in my 25mph restricted neighborhood

It can hustle in 7th with a Bolton upgrade and the big magnet motor. The color KT LCD8H display allows more adjustment on wheel size. Should have mentioned that.