This sizing guide helps you find your ideal Specialized Tarmac SL8 size.
The Tarmac SL8 retains the same geometry as its predecessor, although there is a difference in the stack and reach measurements. Upon further inspection, I found the SL8 and SL7 indeed have the same geometry, taking into account two new measurements, Stack to Stem and Reach to Stem.
Rouleur’s review of the SL8 also confirms this finding.
There are seven Specialized Tarmac SL8 frame sizes for cyclists from 4’8″ to 6’5″ (142 to 196cm). Both S-Works and non-S-Works versions have the same sizing and apply to both male and female cyclists.
|Bike size||Rider height (in)||Rider height (cm)|
|44||4’8″ – 5’1″||142 – 155|
|49||5’1″ – 5’4″||155 – 163|
|52||5’4″ – 5’7″||163 – 170|
|54||5’7″ – 5’9″||170 – 175|
|56||5’9″ – 5’11”||175 – 180|
|58||5’11” – 6’2″||180 – 188|
|61||6’2″ – 6’5″||188 – 196|
Important factors to consider
There’s more to a good fit than height beyond the sizing chart. Here are important things to consider from my experience working at the bike shop selling Specialized bikes.
Specialized sizing vs. other brands
Specialized sizes their bikes such as 44, 49, 52, 54, 56, 58, and 61.
These numbers provide a general indication of the frame size. However, they may not be consistent across other bike brands. What constitutes a size 52 in a Specialized could be different in another model with a similar sizing, such as Cannondale Supersix Evo or Trek Emonda.
Understand the stack and reach measurements
If you’re upgrading from the Tarmac SL7, remember to double-check the stack and reach measurements. The Tarmac SL8 has a higher stack (+10mm) and shorter reach (-3mm) compared to the Tarmac SL7.
If you currently have a bike that fits you well and is comfortable, use that as a reference point.
Find out its Stack and Reach measurements and compare them against the Tarmac SL8’s measurements. Then, pick the closest size.
- Stack is the vertical distance from the bottom bracket to the top of the head tube. Stack height influences how high your handlebars will be relative to your saddle. A higher stack leads to a more upright riding position, which can be more comfortable, especially for longer rides, older riders, and those with less flexibility on the lower back.
- Reach is the horizontal distance from the bottom bracket to the center of the head tube. It determines how stretched or compact your riding position will be. A longer reach results in a more stretched-out, aggressive riding posture, while a shorter reach promotes a more upright position.
The Stack and Reach measurements can be found in the geometry chart below.
Size up or down, if in between sizes?
Compared to other brands, the sizing for Specialized Tarmac SL8 is relatively easy. However, there will be some cyclists that fall right on the upper end of the smaller size and lower end of the larger size.
If that’s you, there are many things to consider, such as your legs-to-torso proportions and the final look of the bike, taking into consideration the number of spacers, stem length, and the amount of exposed seatpost.
Generally, I’d recommend sizing down (go for the smaller of two sizes) for most cyclists.
The smaller frame has more room to extend reach, and increase stack. It’s easier to make a smaller frame bigger than vice versa. However, there is a limit to these corrective measures to avoid having too many spacers (30mm+) or too much exposed seatpost, which makes the bike look out of proportion.
The smaller frame is also stiffer, more maneuverable, and marginally lighter. If set up right, it’ll have more exposed seatpost, leading to more comfort due to increased seatpost flex.
If you have a normal legs-to-torso proportion, opting for the smaller size would be a better choice.
- If you have longer legs with a shorter torso, consider sizing up to avoid having too much exposed seatpost.
- If you have shorter legs with a longer torso, consider sizing down and using a longer stem to extend reach.
Test ride before you buy
Visit your local Specialized dealer to try both sizes. Most Specialized dealers can provide a test ride if they have a bike in your size in their demo fleet. Specialized also conducts a bike demo day annually for you to try out their bikes.
Specialized Tarmac SL8 frame geometry (2020-2023)
The geometry chart below applies to all Specialized Tarmac SL8 frames from the following:
- Years: 2023
- Models: S-Works, Pro, Expert
- Frame material: FACT 12r carbon (S-Works), FACT 10r carbon (Specialized)
|Rider Height (cm)||142 to 155||155 to 163||163 to 170||170 to 175||175 to 180||180 to 188||188 to 196|
|Rider Height (ft)||4’8″ to 5’1″||5’1″ to 5’4″||5’4″ to 5’7″||5’7″ to 5’9″||5’9″ to 5’11”||5’11” to 6’2″||6’2″ to 6’5″|
|Stack to stem (mm)||509||522||535||552||573||599||620|
|Reach to stem (mm)||363||372||377||381||393||400||406|
|Top Tube, Horizontal (mm)||496||509||531||541||563||577||595|
|Seat Tube (mm)||433||445||456||473||494||515||545|
|Seat Tube Angle||75.5º||75.5º||74º||74º||73.5º||73.5º||73º|
|Head Tube (mm)||99||109||120||137||157||184||204|
|Head Tube Angle||70.5º||71.75º||72.5º||73º||73.5º||73.5º||74º|
|BB Height (mm)||266||266||266||268||268||268||268|
|BB Drop (mm)||74||74||74||72||72||72||72|
|Fork Trail (mm)||71||63||58||58||55||55||52|
|Fork Length (mm)||370||370||370||370||370||370||370|
|Fork Offset (mm)||47||47||47||44||44||44||44|
|Front Center (mm)||572||574||577||579||592||606||613|
|Standover Height (mm)||723||735||746||768||786||808||834|
|Stem Length (mm)||80||100||110||70||90||100||110|
|Seatpost Length (mm)||300||380||380||300||300||380||380|
Bernard Lu has 7+ years of experience working in a bicycle shop, overseeing the retail and workshop operations. He’s a qualified bicycle mechanic who understands a cyclist’s needs and speaks the same cycling lingo.
If you meet him at the cafe, he will happily talk to you for hours about all the intricacies of bikes and cycling tech. Just buy him a coffee next time you see him.